Which technique helps to identify a bacterial or viral pathogen in a human body even when its concentration is very low and clinical symptons are not yet visible ?

Options

A. ELISA
B. Total leucocyte count
C. PCR
D. Differential leucocyte count

Answer

To answer the question of which technique helps to identify a bacterial or viral pathogen in the human body even when its concentration is very low and clinical symptoms are not yet visible, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Techniques**: We need to evaluate the four options provided: ELISA, total leukocyte count, PCR, and differential leukocyte count.

2. **Analyzing ELISA**:
- ELISA stands for Enzyme-Linked Immunosorbent Assay.
- It is primarily used to detect antibodies in the blood, which indicates an immune response to pathogens.
- However, it may not be sensitive enough to detect low concentrations of pathogens directly.

3. **Analyzing Total Leukocyte Count**:
- This test measures the total number of white blood cells (WBCs) in the blood.
- While it can indicate an infection if the WBC count is elevated, it does not specifically identify pathogens and may not detect them at low concentrations.

4. **Analyzing PCR**:
- PCR stands for Polymerase Chain Reaction.
- This technique amplifies DNA and can detect very small amounts of bacterial or viral genetic material in a sample.
- It is highly sensitive and specific, making it capable of identifying pathogens even when they are present in low concentrations and before clinical symptoms appear.

5. **Analyzing Differential Leukocyte Count**:
- This test categorizes the different types of white blood cells in the blood.
- While it can provide information about immune responses, it lacks the sensitivity and specificity needed to identify specific pathogens directly.

6. **Conclusion**:
- After analyzing all options, PCR is the most sensitive and specific technique for detecting bacterial or viral pathogens in the human body, even at low concentrations and before symptoms are visible.
- Therefore, the correct answer is **C) PCR**.